DE3928427A1 - Removing heavy metals, esp. mercury from contaminated earth - by repeated washing and fractionation forming conc, fraction for furnace - Google Patents

Abstract

Soil, building rubble or other bulk material contg. heavy metal contaminant, esp. Hg, is initially washed and sieved to produce a finer fraction with enriched metal content. After removal of existing water, this fraction is homogenised by feed water and rewashed in a process combining gravitational and centrifuged feeding, without external power supply. The resulting fine slurry is thermally treated, e.g. in a vertical furnace with multiple superimposed hearths, at temp. appropriate to the particular contaminating metal, with furnace construction modified if necessary. The furnace exhaust gases pass via a venturi washer to a droplet separator collecting the heavy metals. ADVANTAGE - Effective sepn. involves min. power consumption.

Description

The invention relates to a method for cleaning with Heavy metals, especially mercury, contaminated Material such as soil, building rubble, slag, Industrial waste and the like, and a device to carry out the procedure.

The invention has for its object such To design the process so that with one possible low energy consumption a reliable cleaning effect is achieved.

This is achieved in that the Material is washed and sieved to order at a smaller particle size an increased enrichment with the To get heavy metal, what about the heavy metal enriched finer material under gravitational and Centrifugal action washed again without supplying energy and is separated into fractions so that a high degree fine sludge enriched with heavy metal is obtained, which is then by a thermal Treatment from which heavy metal can be cleaned being due to the fine, strong with heavy metal enriched material the thermal separation of the Heavy metal with relatively little energy consumption  can be made.

Advantageous embodiments of the invention are in the following description and specified in the claims.

The invention is illustrated, for example, by the drawing explained in more detail. It shows

Fig. 1 is a schematic flow diagram of a plant for the cleaning of mercury contaminated material

Fig. 2 is a schematic sectional view of a gravity wash,

Fig. 3 is a plan view of the gravity washing installation according to Fig. 2,

Fig. 4 is a detail view of a Wendelabscheiders of gravity washer,

Fig. 5 in a schematic sectional view of a furnace for the thermal treatment of mercury-enriched material, and

Fig. 6 shows a schematic section through a sludge tank.

In Fig. 1, 1 denotes an inlet chute onto which material contaminated with mercury sulfide or mercury compounds, such as soil and building rubble, is placed. This inlet chute 1 is designed as a coarse sieve in order to separate the abandoned soil, for example, into particles larger than 50 mm and smaller than 50 mm. At the same time, the material applied to the inlet chute 1 is washed by a spray device 2 . Particles larger than 50 mm are separated out after washing and discharged into a heap at 3 in the washed and thus cleaned state. The entire wash water and the particles smaller than 50 mm are conveyed into a drum sieve 4 , through which the material introduced is separated into particle sizes up to 5 mm and, for example, from 5 to 20 mm and 20 to 50 mm. During the screening process, the material is washed by a spray device 5 . The washed and thus cleaned of mercury screenings with a particle size of 5 to 20 mm is passed into a hydrocyclone 6 , dewatered in it and then conveyed to a heap at 7. The washed and also cleaned material with a particle size of 20 to 50 mm is discharged at the end of the drum screen 4 and transported to a stockpile at 8 . The inlet chute 1 and the drum sieve 4 are surrounded by a closed trough, so that no contaminated material can escape to the outside.

The remaining mercury-enriched material with a particle size of less than 5 mm passes with the washing water by gravitational action into a hydrocyclone 9 , in which dewatering takes place, whereupon the material is discharged into a mixing cone 10 , in which the water is injected under high pressure Material is thoroughly mixed or homogenized and kept fluid, whereupon it is pumped into a gravity washing system 11 .

The water separated in the two hydrocyclones 6 and 9 is first passed into a settling tank 12 , in which suspended particles can settle in the wash water. The water cleaned by settling is pumped into a fresh water tank 13 .

In the gravitational washing system 11 there is a further separation of the material enriched with mercury into fractions with simultaneous washing of the material without the addition of energy due to gravity and centrifugal action in order to obtain a further enrichment with mercury with the smallest possible particle size.

Details of the gravitational washing system 11 are shown in FIGS. 2 to 4. In the exemplary embodiment shown, four spiral separators 14 are arranged in the block in the gravitational washing system 11 , each of which consists of a spiral groove 15 in a cylindrical shell 16 . Via a manifold 17 coming from the mixing cone 10 material is distributed to the four Wendelabscheider, whereupon the material through the action of gravity along the helical grooves 15 flows down and is divided by centrifugal action into several fractions due to the different specific weight of the components of the material. In the exemplary embodiment shown, three outlets 18 , 19 and 20 are arranged at the lower end of the helical channels in the radial direction over the channel cross section. For example, material enters at the radially inner outlet 20 having a particle size of 2 to 5 mm, while 19 material exits at the outlet mm with a particle size of 1 to 2 and at the outlet 18 particles up to 1 mm, together with the washing water to escape. The material emerging from the spiral separators 14 in fractions reaches an inclined surface 21 , which leads to three series-connected settling troughs 22 , 23 and 24 of a countercurrent sludge separator. Water is injected into the troughs 22 to 24 through an upwardly directed jet nozzle 25 , a maximum water level being maintained along the upper edge of the troughs. In these troughs 22 to 24 , the particles of 0.5 to 5 mm in size settle in accordance with the setting of the water jet nozzles 25 , while fine sludge with a particle size of less than 0.5 mm along the water surface in the troughs to an overflow or outlet port 26 arrives, which is downstream of the troughs 22 to 24 .

As shown in FIG. 1, the material deposited in the troughs 22 to 24 passes into an inclined trough 27 arranged underneath, in which there is a separation between the particles and wash water and, if appropriate, the different particle sizes can also be kept separate. The washing water is passed from the tub 27 into the settling tank 12 , while the washed and thus cleaned particles of 0.5 to 5 mm are discharged onto a stockpile 28 by means of a conveyor belt. The mercury content of the material discharged at 28 is demonstrably less than 5 mg / kg, which is significantly below the permissible limit.

The sludge discharged at the funnel-shaped outlet nozzle 26 with a particle size of up to 0.5 mm has a mercury concentration of 200 to 400 mg / kg with a water content of 70% if, for example, the starting material applied to the inlet chute 1 contaminates with about 90 mg Hg per ton is.

As shown in FIG. 4, a spraying device 29 is provided along the helical trough 15 in the helical separators 14 , by means of which washing water is supplied to the material introduced above, at least in the upper region or also over the length of the helical trough 15 . At the lower end of the helical trough, guide surfaces can be provided in order to guide the individual fractions formed by centrifugal action, which form radially outward in the trough from the center of the spiral separator, into the outlets 18 , 19 and 20 provided for this purpose. Appropriate guides on the surface 21 allow the fractions emerging at the outlets 18 to 20 to be conducted separately into the settling troughs 22 to 24 , so that, for example, the fraction from the outlet 20 into the trough 22 , the fraction from the outlet 19 into the trough 23 and the fraction from the outlet 18 is passed into the trough 24 , while the water surface is connected to all the troughs with the overflow or outlet connection 26 .

According to another embodiment of the gravitational washing system, the outlets 18 to 20 can also be omitted, so that the material divided into fractions reaches the countercurrent sludge separator at the outlet of the helical trough without the individual fractions being kept separate from one another.

While a separation of the material into, for example, three fractions takes place in the spiral separators 14 , a fourth fraction in the form of the sludge heavily enriched with mercury is separated in the downstream countercurrent sludge separator. By adjusting the jet pressure of the nozzles 25 , the particle size can be adjusted, which can settle in the respective trough. At lower, upward jet pressure, finer particles can settle in countercurrent than at higher jet pressure. This setting can be made depending on the material to be treated.

The sludge emerging at the overflow or outlet nozzle 26 and heavily enriched with mercury enters a lamella thickener 30 from which the settled water can be pumped into the settling tank 12 . After standing for 10 to 15 minutes, the sludge has settled in the thickener 30 to such an extent that the water deposited over the sludge is so clear that it can be pumped directly into the fresh water tank 13 .

The sludge concentrated in the lamella thickener 30 with a water content of approximately 60% is pumped by means of a pump 31 into a sludge tank 32 , from which the sludge highly contaminated with mercury is fed via a dewatering screw 33 and a metering screw 34 into a furnace 35 for thermal separation of the Mercury is passed.

In the exemplary embodiment according to FIG. 5, the treatment furnace designed as a shaft furnace is divided into four floors, a fine sieve or a porous plate 36 , which is arranged above a chamber 37 , extending over a partial cross section of the shaft furnace and being introduced into the air which exits through the porous plate 36 and swirls the mud material on the plate. After dewatering in the dewatering screw 33, the sludge material passes from the metering section 34 to the uppermost porous plate 36 , on which the material is swirled by the air flow and is conveyed via a threshold 38 into the remaining passage cross-section 39 , through which it gravitates downward the porous plate 36 'below it falls on the next floor. On the upper floors, the air is introduced into chamber 37 , preheated. In the two middle floors, a burner 54 is provided in order to heat the fine-grained material to a temperature of 700 ° to 750 ° C, while at the same time air is blown preheated in the chambers 37 'and 37 ''. At the passage cross-section 39 '' of the lower burner floor, a plate 40 is provided to reduce heat losses, through which the heated particles reach the porous plate on the bottom floor, through which only cold air is introduced to cool the heated material, the from the bottom floor into a fluidized bed cooler 41 , at the end of which an outlet flap 42 is provided above a conveyor belt.

The very fine-grained material is in the shaft furnace Counterflow through the combustion gases and in crossflow acted upon by the preheated air. Conveniently becomes natural gas for heating as the primary energy source used. Coal or a can be used as a secondary energy source organic portion are used, insofar as Sludge material available.

The shaft furnace is expediently constructed from ring elements, as is indicated in FIG. 5 by the dividing lines between the individual floors. Instead of two burner levels, a single burner level can also be provided.

A smoke exhaust 43 with a built-in Venturi tube 44 is provided above the top floor of the shaft furnace in order to ensure that the exhaust gases are removed properly by building up a negative pressure. In addition, a downstream fan can be provided for extracting the exhaust gases. 45 denotes a heat exchanger in the smoke outlet 43 , by means of which the air introduced into the upper three floors into the chambers 37 can be preheated, as shown schematically in FIG. 1.

In the furnace 35 , the mercury sulfide contained in the material is oxidized at a temperature of 700 to 750 ° C. and converted into metallic mercury, which is removed in vapor form with the combustion gases.

While the fine-grained material discharged from the bottom of the fluidized bed cooler 41 , which has been freed of mercury, is discharged onto a stockpile 46 ( FIG. 1) by means of the conveyor belt, the mercury vapors contained in the exhaust gas are discharged through the smoke outlet 43 at the top, the exhaust gas also containing dust components that are carried away by the air movement.

From the smoke vent 43 , the exhaust gases first enter a venturi scrubber 47 , in the inlet area of which a nozzle lance (not shown) is provided, through which the exhaust gas is cooled. The Venturi scrubber 47 is designed so that the exhaust gases always hit a water-sprayed surface. This ensures that dust does not stick to the wall of the scrubber. The washing water enters an upper cylindrical part of the Venturi scrubber, for example, tangentially at three points and flows as a closed water film in the conical part to the constriction of the Venturi nozzle, in which the exhaust gas reaches its maximum speed. The water film, which is closed to the bottleneck, is divided into the finest water droplets by the exhaust gas flow, the size and number of which depends on the flow velocity and thus on the differential pressure of the Venturi scrubber. Due to the resulting relative velocity between water droplets and dust particles in the exhaust gas, dust particles can accumulate on the water droplets, so that they can be separated in a downstream droplet separator known per se.

The mercury is separated in such a way that due to the drop in temperature between laundry and The vaporous components condense out of the scrubber and form droplets, which are then also in the downstream droplet separator.

The water from the Venturi scrubber 47 with dust particles and mercury particles reaches a collecting container 48 , above which a droplet separator 49 ( FIG. 1) is arranged, in which the remaining exhaust gas is cooled from approximately 600 ° C. to approximately 30 ° C. Droplets and particles still present in the exhaust gas are returned from the droplet separator 49 into the Venturi scrubber 47 and subjected to the washing treatment again. To ensure that no mercury vapors are released into the environment, the cover of the collecting container 48 is provided with a ventilation line 50 ( FIG. 1) which is connected to the inlet side of the venturi scrubber 47 . Due to the negative pressure on the inlet side of the Venturi scrubber, a flow to the Venturi scrubber is forced, so that if there is a leak at the collecting container 48, a flow is always forced from the outside inwards.

The separation between mercury, sludge and washing liquid takes place in the collecting container 48 . In order to achieve a high degree of separation in mercury separation, wash water of approx. 18 ° C is used, with which the Venturi scrubber is supplied in a single pass.

A collecting vessel 51 is provided under the collecting container 48 for the separated mercury, which can be recycled. At the top of the droplet separator 49 , the cooled exhaust gas is passed through a line 52 to an exhaust gas cleaning system, which can be designed in a manner known per se. Expediently, dust filters and activated carbon filters are provided so that the exhaust gas can then be discharged into the environment.

Individual facilities of the system can be designed in different ways. The inlet chute 1 expediently has transverse iron bars on which the material is held for a certain time, for example 20 seconds, and is washed by constant spraying before it is discharged between the bars or conveyed into the drum screen 4 . The size of the material to be screened can be adjusted by adjusting the distances between the iron bars.

Advantageously, the drum screen 4 is preceded by a closed, rotating drum in order to dissolve and grind up lumps of earth. The circumferential closed drum can be provided on the inner circumference with protruding elements that act as a lifter. In order to control the throughput speed of the material introduced, a retaining ring with a height of approximately 50 mm can be attached at the end of this first closed section, which is followed by the actual screen surface in the form of a rotating screen drum. This storage ring ensures a longer dwell time and a better grinding effect in the first section, whereby the material can also be sprayed with washing water. After the material to be sieved has reached the sieving surface via the damming ring, it is gripped by a strong water jet at an angle of approximately 15 ° and rotated around its own axis in order to ensure an effective washing process and a good sieving effect. Advantageously, lifting elements are provided on the inner circumference of the screening drum in order to be able to discharge screenings with a particle size of 20 to 50 mm by the rotary movement of the drum at its end. Another storage ring can in turn be provided at the outer end of the drum in order to increase the dwell time of the material to be screened in the drum and to ensure a good washing effect. The material discharged at the end of the drum has only a low residual moisture due to its long path. The spray angle of the nozzles in the screen section is expediently adjustable, for example up to 25 °. The sieve section of the sieve drum 4 is expediently divided into sections with different sieve sizes, so that, for example, particles up to 5 mm in a first section and particles of 5 to 20 mm can pass through the sieve in a subsequent section. Material from 20 to 50 mm is ejected at the end of the drum.

The sludge tank 32 , which acts as a buffer tank for supplying the furnace 35 , is expediently designed in the manner shown schematically in FIG. 6. Arranged in the sludge tank 32 is a compression screw 54 driven by a motor, which presses the sludge into a funnel-shaped outlet which opens into the drainage screw 33 . At the upper edge of the sludge tank, an overflow ring 55 is provided, in which the clear water formed by settling collects, which can be returned to the fresh water tank 13 . At the end of the dewatering screw 33 driven by a motor there is a flap 56 provided with a counterweight, the compressed sludge being removed from the dewatering screw by lifting the flap 56 and being fed to the dosing screw 34 . At 57 , the water is drained off. The dosing screw 34 is connected directly to the furnace 35 and forms a closure for the interior of the furnace, so that even in the event of malfunctions, uncleaned exhaust gases cannot escape through the dosing screw.

In order to limit the fresh water requirement of the plant, a closed water cycle is provided. It is only necessary to re-supply the holding water discharged with the screenings disposed of and the water evaporated during the thermal treatment. The closed water cycle can be divided into sub-cycles, since clean water does not always have to be used for wet screening and washing. Experiments have shown that just by standing the washing water in the settling tank 12, very low Hg values can be achieved in the process water.

The sludge settled in the settling tank 12 is pumped from time to time directly into the lamella thickener 30 and processed further with the sludge settled there. If, after repeated use, the wash water reaches an excessively high degree of saturation, so that the settling time would take too long, it is pumped into the sludge container 32 together with the highly contaminated sludge.

The water accumulating in the dewatering screw 33 connected to the sludge tank 32 is first led into the settling tank 12 and from there back into the fresh water tank.

The venturi washer 47 is supplied with cool water, for example well water. The washing water from the Venturi scrubber is expediently returned to the fresh water container via an intermediate container 53 , it being possible to check in the intermediate container 53 whether sludge contaminated with mercury settles out. For this purpose, the intermediate container 53 is divided into an upper and a lower section with a connecting pipe and a flap valve therein, the upper section containing the water overflowing from the collecting tank 48 , which flows through the connecting pipe into the lower section in which the Control after contaminated sludge is made. Should contaminated sludge settle in the lower section of the intermediate container 53 , the flap valve in the connecting pipe is closed and the contaminated water is led into the sludge container 32 .

The system described is suitable not only for cleaning soil, building rubble and the like from mercury, but also from other heavy metals, in the case of other heavy metals the temperature in the treatment furnace 35 is set accordingly and its structure can be modified.

In particular, the gravitational washing system 11 or the shaft furnace 35 can also be used advantageously in conjunction with other systems. The gravitational washing system 11 achieves a very effective separation into fractions without the supply of energy, so that this gravitational washing system can also be used, for example, only for washing and separating. The structure of the shaft furnace 35 also enables a very effective thermal treatment of fine-grained material, which can also have a different composition than the one specified.

Claims (12)

1. A method of cleaning with heavy metals, especially mercury, contaminated material such as soil, building rubble and the like, characterized in that the material is washed and sieved, whereupon the finer material enriched with the heavy metal washed again under the action of gravity and centrifugal force and in Fractions is divided in order to obtain a further accumulation of heavy metal in fine sludge, and that the sludge enriched with the heavy metal is freed from the heavy metal by thermal treatment. 2. The method according to claim 1, characterized, that after the washing and sieving process, the finer, enriched material drained and renewed by Water supply is homogenized before it is washed and separation process under gravitational and Centrifugal force is subjected. 3. The method according to claims 1 and 2, characterized, that after washing and separating Gravitational and centrifugal force effect the material for separating coarser particles over a water surface is led, under which an upward Countercurrent is generated, which on this Fine material overflowing and drained of water is then thermally treated.   4. The method according to the preceding claims, characterized, that the enriched and dewatered sludge material countercurrent to combustion gases through an oven is directed, while at the same time air in the Material flow for the swirling is initiated. 5. The method according to the preceding claims, characterized, that the exhaust gases emerging from the furnace via a Venturi scrubber with a droplet separator Sedimentation tanks for the separation of heavy metals are fed. 6. The method according to the preceding claims, characterized, that for the washing and separation processes wash water in closed cycle and after weaning of the used wash water used again becomes. 7. The device, in particular for carrying out the method according to claim 1, characterized by at least one helical groove ( 15 ) in an outer circumference of the helix ( 14 ) surrounding the sheath ( 16 ), with an inlet at the top of the helix and an outlet at the bottom End of the coil, through at least one separating trough ( 22-24 ) arranged below the coil ( 14 ) with a device ( 25 ) for generating an upward counterflow, and through an overflow ( 26 ) on the trough for discharging the undeposited material . 8. The device according to claim 7, characterized in that a spraying device ( 29 ) is provided at least over a portion of the helical groove ( 15 ). 9. Device according to claims 7 and 8, characterized in that at the lower end of the helical groove ( 15 ) in the radial direction distributed outlets ( 18 , 19 , 20 ) are provided. 10. The device, in particular for carrying out the method according to claim 1, characterized by an oven ( 35 ) divided into a plurality of floors arranged one above the other, a porous plate ( 36 ) extending over a partial cross section of the oven being provided on each floor, through which Air can be supplied via a chamber arranged underneath, and the porous plate of the following floor is arranged under a passage ( 39 ) next to the porous plate of one level, and through a burner ( 54 ) on at least one of the middle levels. 11. The device according to claim 10, characterized in that a metering screw ( 34 ) is connected to the upper part of the furnace ( 35 ), which forms a gas-tight seal for the furnace. 12. Device according to claims 10 and 11, characterized in that at the lower end of the furnace a fluidized bed cooler ( 41 ) with a controllable outlet flap and on the upper part of the furnace a gas outlet ( 43 ) with a venturi tube ( 44 ) is connected .